Abstract
OCTN2 - the Organic Cation Transporter Novel family member 2 (SLC22A5) is known to be a xenobiotic/drug transporter. It transports as well carnitine - a compound necessary for oxidation of fatty acids and mutations of its gene cause primary carnitine deficiency. Octn2 regulation by protein kinase C (PKC) was studied in rat astrocytes - cells in which β-oxidation takes place in the brain. Activation of PKC with phorbol ester stimulated L-carnitine transport and increased cell surface presence of the transporter, although no PKC-specific phosphorylation of Octn2 could be detected. PKC activation resulted in an augmented Octn2 presence in cholesterol/sphingolipid-rich microdomains of plasma membrane (rafts) and increased co-precipitation of Octn2 with raft-proteins, caveolin-1 and flotillin-1. Deletion of potential caveolin-1 binding motifs pointed to amino acids 14–22 and 447–454 as the caveolin-1 binding sites within Octn2 sequence. A direct interaction of Octn2 with caveolin-1 in astrocytes upon PKC activation was detected by proximity ligation assay, while such an interaction was excluded in case of flotillin-1. Functioning of a multi-protein complex regulated by PKC has been postulated in rOctn2 trafficking to the cell surface, a process which could be important both under physiological conditions, when carnitine facilitates fatty acids catabolism and controls free Coenzyme A pool as well as in pathology, when transport of several drugs can induce secondary carnitine deficiency.
Highlights
Several solute transporters are important for proper functioning of astrocytes, their activity is a necessary prerequisite of a close cooperation in the brain between astrocytes and neurons, just to mention maintenance of neurotransmitters pool
If Octn2 can be phosphorylated by protein kinase C (PKC), the cell extracts obtained at all experimental conditions were subjected to immunoprecipitation
We further verified the phosphorylation status of proteins co-precipitating with Octn2 using two different clones of anti-phosphoserine antibodies recognizing phosphoserine in a vicinity of positively charged amino acids, a consensus site recognized by PKC [39]
Summary
Several solute transporters are important for proper functioning of astrocytes, their activity is a necessary prerequisite of a close cooperation in the brain between astrocytes and neurons, just to mention maintenance of neurotransmitters pool. Organic cation/carnitine transporter OCTN2 [1,2,3], coded by SLC22A5 gene, belongs to a superfamily of organic ion transporters, specific towards organic anions (OATs), urate (URAT) and organic cations (OCTs and OCTNs) for review see, [4]. OCTN3 has been postulated to function as a peroxisomal carnitine transporter [6,7]. OCTN2, in a Na+-independent way, transports a broad spectrum of organic cations, including xenobiotics/drugs as substrates [8,9,10]. It transports as well carnitine, but in a Na+-dependent way [1,2] and mutations in SLC22A5 gene can cause systemic carnitine deficiency, classified as an inherited disease OMIM212149 [11]. OCTN2 is ubiquitous in the peripheral tissues and it was found to be present in the brain and in cultured astrocytes [6,12,13,14]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
